Modeling of material recovery facility performance with applications for life cycle assessment

Abstract

Single stream recycling programs improve participation rates and divert more end-of-life products from landfill to recycling. The resulting mixture of waste must be sorted, however, before individual materials can be reprocessed for recycling. Material recovery facilities (MRFs) use a series of mechanical and manual sorting steps to separate the mixed stream of materials. The ability of MRFs to correctly sort materials is therefore a critical component of recycling systems. In this thesis, we apply a network flow model to evaluate the performance of sorting facility scenarios. We use experimental sorting efficiencies obtained through waste sampling at a functioning MRF, and explore how those efficiencies change under different operating conditions. We further apply the model to find the best configuration of a series of sorting units, optimizing for both profit and overall sorting efficiency. Recycling is promoted by the EPA and other organizations as a means of reducing the impact of material use. The benefits of recycling relative to landfill and incineration are determined using life cycle analysis (LCA), which takes into account material recovery rates. We apply modeled recovery rates for selected materials to a recycling LCA, and show that they directly impact the magnitude of estimated benefits.